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A294124
Numbers k such that (13*10^k + 179)/3 is prime.
0
1, 5, 8, 21, 37, 61, 62, 126, 188, 221, 253, 523, 654, 1875, 2372, 2394, 3073, 4158, 6663, 6881, 167911
OFFSET
1,2
COMMENTS
For k > 1, numbers k such that the digit 4 followed by k-2 occurrences of the digit 3 followed by the digits 93 is prime (see Example section).
a(22) > 2*10^5.
EXAMPLE
5 is in this sequence because (13*10^5 + 179)/3 = 433393 is prime.
Initial terms and associated primes:
a(1) = 1, 103;
a(2) = 5, 433393;
a(3) = 8, 433333393;
a(4) = 21, 4333333333333333333393;
a(5) = 37, 43333333333333333333333333333333333393; etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(13*10^# + 179)/3] &] (* corrected by Georg Fischer, Jul 22 2019 *)
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Oct 23 2017
EXTENSIONS
a(21) from Robert Price, Nov 17 2018
STATUS
approved